The present invention relates to a method and an apparatus for correcting or compensating a cutter position for a radial deflection, in which a tyre surface subjected to cutting deviates in the radial direction, and/or a lateral deflection, in which a tyre surface subjected to cutting deviates in the lateral direction, in a tyre grooving operation.
An apparatus for grooving in a tread surface of a new tyre or a re-treaded tyre has, in general, a tyre supporting shaft, which supports a tyre in a vertical posture, and a cutter unit, of which at least the lateral movement in the direction parallel with the tyre supporting shaft and the radial movement in the direction perpendicular to the tyre supporting shaft are allowed.
However, a tyre itself, in general, does not have an accurate roundness, a tyre tread surface is sometimes inclined to a certain degree and the tyre is sometimes supported in a deviated condition and therefore, a radial distance from the center of the tyre supporting shaft to the tread surface is not constant. Accordingly, radial deflection of the tread surface in the radial direction is caused. In the above situation, a tyre grooving, wherein the cutter movement is controlled in accordance with a prespecified tread pattern shape by a set-up program with a tyre being rotated, cannot provide constant groove depths for each tyre having same size and same specification. Moreover, even if a plurality of grooves having a mutually uniform depth on the left and right sides of the tyre equator are required to be formed on one tyre, the depths of the grooves on the left side of the equator differ from those on the right side. Thus there is caused a problem in quality that the stability of the tyre is impaired and the strength thereof is lowered.
Further, if distortion of, the tyre itself and deviation in the tyre supporting cause a lateral deflection of the side surface of the tyre in the direction of the tyre width, a tyre grooving, wherein the cutter movement is controlled in accordance with a prespecified tread pattern shape by a set-up program with a tyre being rotated, cannot make a groove position keep a constant relationship to the tyre tread center for each tyre having same size and same specification. Moreover, a deviation of the tyre tread center in one tyre sometimes results. Thus there is caused a problem in quality that the stability of the tyre is impaired and the strength thereof is lowered.
In this connection, there has been proposed another apparatus, for example, as disclosed in Japanese Unexamined Patent Publication No. 74635/1987, wherein there is provided a non-contact type detecting means for detecting the shape of the tread surface, and the cutter position is controlled based on the detected data so that the amount of rubber being cut off from the tyre is kept constant.
However, suchlike apparatus has a problem that a large frame for mounting the detecting means are required.
Further the groove depth cannot be kept constant along the entire circumferential length of the groove which is formed on the entire periphery in the circumferential direction of the tyre because the cutter position in the direction of the cutting depth is kept constant only at the beginning of the cutting operation.
Moreover, an image detector is used and the cutter position in the cutting operation is determined by calculation based on the area of the tyre exposed to the view of the detector in order to allow the constant amount of rubber to be cut off. However, the determination of the cutter position by calculation based on the area is very difficult particularly when the cutter acrosses another groove which has been formed already or when the radial fluctuation on the right side of the tyre equator is different from that on the left side, even if the constant amount of rubber to be cut off is purposed. Since the cutter position is not movable in accordance with the radial deflection of the tyre, the groove depth and the groove width cannot be kept at respective desired constant values by following the radial deflection of the tyre.
Still further, since the cutter position cannot be moved in accordance with the lateral deflection of the tyre, the groove position relative to the tread center cannot be kept at a desired constant value by following the lateral deflection of the tyre.
An object of the present invention is to provide a method and an apparatus for grooving which provide a groove having desired constant depth and width and being formed at a desired constant position even in case that a tyre has a radial deflection and/or a lateral deflection.